My guess is fuel pump is weak, need to know how much pressure it has!
JUST REPLACE THE PUMP! GM 11 years old, i bet that is what it is going to take to fix your truck!!!
Done been there lots of times. It can be off by 3 psi. and it aint going to run!

Got PULSE?....... Are injectors working? If it has fuel pressure and spark and will run by spraying ether or carb. spray into it , then maybe no signal to injectors?.....No air leaks between mass air flow and throttle body? That will also stop or greatly reduce fuel delivery. Do you have 2 vans both a 2000 and a 2001? your post has both years on it and if you do and they are both 5.7L , then maybe you can swap MAF and see if that does the trick.